Method for protecting at least one consumer against overvoltage tages and device for carrying out the method

ABSTRACT

A method and a device for protecting at least one consumer against overvoltages when working with a method for non-contact transmission of electric power from one or more medium-frequency current sources, whose frequencies may have deviations around medium frequency f M , to the at least one moving consumer via one or more transmission lines and transformer heads, allocated to the consumers, having a downstream matching controller for adjusting the power received from the transmission line; a transmission line is fed from a medium-frequency current source with a medium-frequency current that is constant in its effective value during the power transmission; the respective consumer is supplied with energy by at least one matching controller having at least one feed-in; one or more fed currents are rectified in each instance in a rectifier, smoothed in each instance by a link-circuit reactor and brought together; with the aid of a switch, the link-circuit current, brought together in each instance, is either supplied to a link-circuit capacitor buffering output voltage U =  of the matching controller, or is shunted upstream of the link-circuit capacitor, depending upon the power demand of the consumers; and the voltage U =  at at least one link-circuit capacitor is compared to a predefinable value, and if this value is exceeded, an electronic power circuit-breaker is turned on for shunting the link-circuit current.

[0001] The present invention relates to a method for protecting at least one consumer against overvoltages and a device for carrying out the method.

[0002] The German Patent 197 35 624 C1 describes a method for the non-contact transmission of electric power from a medium-frequency current source having a medium frequency f_(M) to one or more moving consumers via a transmission line, and from transformer heads, allocated to the moving consumers, having a downstream matching controller for adjusting the power received from the transmission line, the transmission line being fed from the medium-frequency current source with a medium-frequency current that is constant in its effective value during the power transmission.

[0003] The matching controller converts the medium-frequency current, injected from the transformer head, into a DC voltage. As described in FIGS. 3, 7a and 7 b and the associated specification of DE 197 35 624 C1, switch T_(s) is operated synchronously with respect to the characteristic, and with double the frequency of the input current of the matching controller. However, an important disadvantage is that this high switching frequency 2 f_(M) results in high switching losses. Another disadvantage is that the synchronous principle can no longer be maintained when using a plurality of asynchronously operating feed-ins for supplying a matching controller.

[0004] In the case of DE 197 35 624 C1, a relay is used which, after the matching controller is switched in, goes into the blocking state with low voltage. Upon switch-off or in response to a short-circuit in the region of this low voltage, the relay returns again to the conductive state. It is disadvantageous that the relay is subject to mechanical wear, and therefore may lead to an accident. It is also disadvantageous that in DE 197 35 624 C1, in case of an emergency, a dangerously high voltage may occur at the consumer, which may lead to accidents.

[0005] Therefore, the object of the present invention is to increase safety when working with a matching controller; in particular, the intention is to avoid the danger of fire in the event of an emergency or during unusual operating conditions.

[0006] The objective is achieved according to the present invention in the case of the method for protecting at least one consumer from overvoltages, according to the features indicated in claim 1, and in the case of the device for use when working with such a method, according to the features indicated in claim 13.

[0007] Essential features of the invention with respect to the method for non-contact energy transmission are that from one or more medium-frequency current sources, whose frequencies may have small deviations around medium frequency f_(M), to at least one moving consumer via one or more transmission lines and transformer heads, allocated to the consumers, having a downstream matching controller for adjusting the power received from the transmission line; a transmission line is fed from a medium-frequency current source with a medium-frequency current that is constant in its effective value during the power transmission; the respective consumer is supplied with energy by at least one matching controller having at least one feed-in; one or more fed currents are rectified in each instance in a rectifier, smoothed in each case by a link-circuit reactor and brought together; with the aid of a switch (S, V1), the link-circuit current, brought together in each instance, is either supplied to a link-circuit capacitor buffering output voltage U₌ of the matching controller, or is shunted upstream of the link-circuit capacitor, depending upon the power demand of the consumers; and voltage U₌ at at least one link-circuit capacitor is compared to a fixed or pre-definable value, and if this value is exceeded, an electronic power circuit-breaker (V4, Thy) is turned on for shunting the link-circuit current.

[0008] In this context, it is advantageous that the overvoltage protection becomes active in case of an emergency. For example, such a case of emergency exists in the event the low voltage supply for the driving of switch (S, V1) fails, or given a controller defect or the like. In that case, the voltage at the link-circuit capacitor increases and may reach dangerous values. This may possibly happen if the entire system is overloaded and/or when the matching controller is under-supplied, as well. In these cases, the link-circuit current is then advantageously shunted, and a further increase of the voltage at the link-circuit capacitor is prevented.

[0009] Another advantage is that the overvoltage protection is executable in a wear-free fashion, and it is not necessary to use any mechanical parts such as relays or the like. In particular, sparking is prevented, and operation is made possible in areas at risk for explosion.

[0010] In emergency cases which are not caused by breakdown or destruction, after resetting the matching controller or after shutting down the system and/or eliminating the cause, reuse of the matching controller is even advantageously feasible.

[0011] In one advantageous specific embodiment of the present invention, the electronic power circuit-breaker is a thyristor which, after firing, is only blocked upon disappearance of the current shunted through it. The advantage here is that it is cost-effective, and after firing, no further driving is necessary.

[0012] In one advantageous specific embodiment of the present invention, the signal electronics for generating the driving signal for the electronic power circuit-breaker are supplied from the voltage at the link-circuit capacitor. This has the advantage that no special voltage supply such as an emergency battery or the like is necessary.

[0013] According to one advantageous specific embodiment of the present invention, the signal electronics for generating the driving signal for the electronic power circuit-breaker include a positive feedback. Of advantage in this case is that after the critical voltage has been exceeded, the overvoltage protection is activated and stabilizes itself.

[0014] In one advantageous specific embodiment according to the present invention, the respective switch is switched in such a way that switching frequency 1/T is less than double the medium frequency, thus, 1/T<2 f_(M).

[0015] In this context, it is advantageous that the switching losses are less than for methods which assume a switching frequency of 2 f _(M), and that not only synchronously operating, but also a plurality of asynchronously operating feed-ins are usable for supplying a matching controller. In addition, the current flow is controllable by a single switch.

[0016] According to one advantageous specific embodiment of the present invention, switching frequency 1/T is selected as a value between 0.5 f_(M) and 1.5 f_(M). The advantage here is that it is possible to use a link-circuit reactor having the smallest possible size, accompanied by the lowest possible switching losses.

[0017] In one advantageous specific embodiment of the present invention, the switch is switched periodically with a frequency 1/T and asynchronously with respect to one or more medium-frequency feed-ins in such a way that there is no constant phase relationship to the currents of one or more feed-ins. The advantage in this case is that the method is robustly executable, and it is possible to save on means for synchronization.

[0018] In one advantageous specific embodiment according to the present invention, the link-circuit reactor is designed in such a way that the link-circuit current does not pulsate during operation. The advantage here is that a continuous power flow is ensured in spite of the aforesaid low switching frequency.

[0019] According to one advantageous specific embodiment of the present invention, the frequencies of the medium-frequency feed-ins have deviations around f_(M). The advantage in this context is that the feed-ins do not have to be synchronized with each other.

[0020] Essential features of the invention with respect to the device are that the means for driving the respective switch include no means for synchronization to the medium-frequency feed-ins of advantage here is that the driving is simple, cost-effective and, in particular, robust with respect to interference effects when working with asynchronously operating feed-ins.

[0021] In one advantageous specific embodiment according to the present invention, the anode voltage of thyristor (Thy, V4) corresponds to the maximum from voltage at the link-circuit capacitor and voltage at switch (S, V1). This offers the advantage that no dangerously high voltage changes per time occur at the thyristor.

[0022] According to one advantageous embodiment of the present invention, the anode of the thyristor is connected via a diode to at least one link-circuit reactor and/or the anode of the thyristor is connected via a resistor R1 to link-circuit capacitor C6. The advantage in this case is that the diode decouples the region of the current rectified by the link-circuit reactor and the region of the consumer voltage. Consequently, in the blocking state, the thyristor is advantageously supplied with a voltage without dangerously high voltage changes per time, and in the conductive state, the link-circuit current is able to be shunted via the thyristor with the aid of the indicated diode.

[0023] In one advantageous specific embodiment of the present invention, the means for driving the respective switch include a modulator having rising and falling edges running in a linear fashion over time, the amount of the gradient of the rising and falling edges being selectable to be different. The advantage in this case is that, in particular, a sawtooth-shaped modulator signal may be used which is inexpensive and uncomplicated to generate.

[0024] In one advantageous specific embodiment according to the present invention, a matching controller has a plurality of feed-ins, that in each case feed a rectifier, whose output currents are in each instance brought together via a link-circuit reactor, and a switch is connected in series in such a way that the link-circuit current is either supplied to a link-circuit capacitor buffering output voltage U₌ of the matching controller, or is shunted upstream of this link-circuit capacitor, depending on the power demand of the consumer connected to the matching controller. This has the advantage that not only synchronously operating, but also asynchronously operating feed-ins may be used.

[0025] In one advantageous specific embodiment according to the present invention, the output voltages of two or more matching controllers are parallel-connected via diodes for supplying a consumer. The advantage in this case is that the power able to be made available may be increased as needed.

[0026] In another advantageous embodiment of the present invention, the anode of the thyristor is connected via a diode V3 to at least one link-circuit reactor. Of advantage here is that a decoupling of the alternating component, particularly of the high-frequency voltage component, is therefore attainable.

[0027] In a further advantageous embodiment of the present invention, the anode of the thyristor is connected via a resistor R1 to link-circuit capacitor C6. This offers the advantage that the voltage change per time dU/dt is able to be limited below a critical value, such that no firing of the thyristor is triggered as a result of such critically high voltage changes per time dU/dt.

[0028] Reference Numeral List

[0029]1 infeed controller (ESS)

[0030]2 gyrator

[0031]3 matching transformer

[0032]4 transmission line

[0033]5 transformer head with power factor correction capacitor

[0034]6 matching controller (APS)

[0035]7 consumer

[0036]21 feed-in

[0037]22 rectifier

[0038]23 link-circuit reactor

[0039]25 switch

[0040] S, V1 switch

[0041]26 diode

[0042] C6, 27 link-circuit capacitor

[0043] I₌ output current of the matching controller

[0044] I_(Z) link-circuit current

[0045] I_(ZV) smoothed signal of the link-circuit current

[0046] I_(SZ) sawtooth-shaped modulator signal

[0047] I_(ST) control signal

[0048] I_(A) current source, output current of the gyrator

[0049] I_(Ü) current in the transmission line

[0050] U_(setpoint) setpoint voltage

[0051] U₌ output voltage of the matching controller

[0052] U_(A) output voltage of the infeed controller

[0053] C_(G) gyrator capacitance

[0054] L_(G) gyrator inductance

[0055] Ü transformation voltage ratio of the matching transformer

[0056] w₂ number of turns of the transformer head

[0057] f_(M) medium frequency

[0058] K_(D) gain of the attenuator

[0059] K_(U) gain of the voltage controller

[0060] T₂ time constant of the attenuator

[0061] T₃ delay-time constant of the connection-of-load

[0062] S_(on) trip-on signal for switch

[0063] R1, R2, R3, R4, R5, R6, R7, R8, R9 resistor

[0064] C1, C2, C3, C4, C5 capacitor

[0065] V2, V3, V7 diode

[0066] V4 thyristor

[0067] V5 field-effect transistor

[0068] V6 transistor

[0069] V8 Zener diode

[0070] N1 shunt regulator

[0071] The invention shall now be explained in detail with reference to the figures.

[0072]FIG. 1 shows an exemplary schematic diagram for non-contact energy transmission having a matching controller 6.

[0073]FIG. 2 shows an exemplary schematic diagram of the matching controller with thyristor for protection against overvoltages.

[0074]FIG. 3 shows a schematic diagram of the control and driving of the matching controller for an exemplary embodiment.

[0075]FIG. 4 shows the generation of the requisite thyristor driving signal.

[0076]FIG. 5 shows an exemplary circuit diagram of the entire overvoltage protection according to the present invention.

[0077]FIG. 1 shows a first exemplary schematic diagram for non-contact energy transmission having a matching controller 6. It includes a stationary part and a movable part.

[0078] The stationary part includes an infeed controller 1, a gyrator 2, a matching transformer 3 and a transmission line 4.

[0079] Infeed controller 1 converts the low-frequency AC voltage received from three-phase system (L1, L2, L3) into a medium-frequency voltage U_(A) having a constant medium frequency f_(M) of, for example, 25 kHz. A resonantly operated series resonant circuit, so-called gyrator 2, connected in series to infeed controller 1, represents a voltage-controlled current source I_(A). Gyrator capacitance C_(G) and gyrator inductance L_(G) are rated in accordance with medium frequency f_(M) and the nominal power of infeed controller 1.

[0080] Current source I_(A) feeds a matching transformer 3 whose transformation voltage ratio Ü is such that a medium-frequency current I_(Ü), which is constant in its effective value, flows in transmission line 4, regardless of the nominal power of infeed controller 1.

[0081] The movable part includes a transformer head 5 having a power-factor correction capacitor, a matching controller 6 and a consumer 7. Transmission line 4 has an elongated conductor, to which coil windings of transformer head 5 are inductively coupled in such a way that energy is transmitted to the movable part. In this context, transformer head 5 has a number of turns w₂, which determines the current intensity of a feed-in at matching controller 6.

[0082] Matching controller 6 converts the medium-frequency current, injected from transformer head 5, into a DC voltage U₌. In one exemplary embodiment, this voltage is used for feeding a conventional frequency converter as consumer 7, in order to implement a speed-adjustable drive on the movable part.

[0083] The current transferred from transmission line 4 to transformer head 5 represents a feed-in 21. According to FIG. 2, this current is rectified in a rectifier 22 of matching controller 6, is smoothed by a link-circuit reactor 23, and with the aid of a switch 25, is either supplied to link-circuit capacitor 27 buffering output voltage U=of matching controller 6, or is shunted upstream of this link-circuit capacitor 27, depending on the power demand of consumer 7 connected to matching controller 6.

[0084] In addition, FIG. 2 shows a thyristor Thy as electronic power circuit-breaker, with which, via diode V3, the current, smoothed by link-circuit reactor 23, is able to be transmitted in the event of an unacceptably high output voltage U₌, thus an overvoltage, occurring at consumer 7. The generation of requisite driving signal Thy_(on) of thyristor Thy is sketched in FIG. 4. In this context, output voltage U₌ is compared to a maximum allowed voltage value U_(Max). If this maximum allowed voltage value U_(Max) is exceeded, thyristor Thy is then fired. Only when the current shunted through the thyristor disappears or becomes less than the holding current does thyristor Thy block again. This is able to be effected, for example, in that switch (S, V1) is closed.

[0085]FIG. 2 also shows a resistor R1 which eliminates or at least sharply reduces the fluctuations in the voltage applied at thyristor Thy, in particular strongly attenuates the high-frequency component of the voltage applied at thyristor Thy.

[0086] In cases of emergency, such as an overloading of the infeed controller, an under-supply of the matching controller, a short-circuit in the low-voltage supply of the signal electronics of the matching controller, which are used for generating the driving signals for switch (S, V1), or in the event of a failure of an essential part in these signal electronics, the voltage at the link-circuit capacitor may reach dangerously high values and lead to damages. The overvoltage protection of the present invention prevents such damages.

[0087]FIG. 3 shows a schematic diagram of the control and driving of switch 25 of the matching controller for an exemplary embodiment. Non-linear elements are double-framed, and linear elements are single-framed.

[0088] The linear part includes the following components: P-voltage controller of gain K_(U), connection-of-load with a delay time constant T₃, and attenuator, including time-delay element with time constant T₂ and proportional element of gain K_(D).

[0089] The non-linear part includes a modulator and a two-point element which generates a trip-on signal S_(on) for switch 25. The input quantity of the two-point element is formed from the difference between a sawtooth-shaped modulator signal I_(SZ) and a control signal I_(ST).

[0090] The amplitude of the sawtooth-shaped modulator signal is determined by smoothed signal I_(ZV) of the link-circuit current. Frequency 1/T of the modulator signal is predefined asynchronously with respect to frequency f_(M) of feed-in 21.

[0091] Control signal I_(ST) is made of the sum of the output signals of the P-voltage controller, the connection-of-load and the attenuator.

[0092] The output signal of the P-voltage controller is yielded by the difference, weighted by a proportional element, between setpoint voltage U_(setpoint) and output voltage U₌ of the matching controller.

[0093] To form the output signal of the connection-of-load, output current I₌ of the matching controller is supplied to a time-delay element having delay time T₃.

[0094] The output signal of the attenuator is yielded by the difference, weighted by a proportional element, between link-circuit current I_(Z) and smoothed signal I_(ZV) of the link-circuit current. The gain of the proportional element is K_(D).

[0095] The control and driving ensure the following advantageous functions:

[0096] The voltage controller is designed as a simple P-controller, since the connection-of-load preselects trip-on signal S_(on) of switch 25 in a pre-controlling manner, which means the voltage controller is substantially unloaded.

[0097] The attenuator damps natural oscillations of link-circuit current I_(Z) in the oscillatory configuration composed of inductive transformer head 5 with power factor correction capacitor, rectifier 22 and link-circuit reactor 23.

[0098] The attenuator damps natural oscillations of link-circuit current I_(Z) in the oscillatory configuration composed of inductive transformer head 5 with power factor correction capacitor, rectifier 22 and link-circuit reactor 23.

[0099] In other exemplary embodiments of the present invention, instead of sawtooth-shaped modulator signal I_(SZ), a periodic modulator signal having rising and falling edges running in a linear fashion over time may be used, the amount of the gradient of the rising and falling edges being selectable to be different. If the amount of the gradient of the two edges is equal, a triangular characteristic results.

[0100] Thus, in contrast to German Published Patent Application No. 197 35 624, not only may such a triangular modulator signal be used, but also in particular the sawtooth-shaped modulator signal which is easy to generate and is used in the exemplary embodiment of the present invention.

[0101] In the exemplary embodiments according to the present invention, amplitude and period duration T are each selected as in the case of the sawtooth-shaped modulator signal described. In this context, period duration T is selected as a fixed value from a 10%-wide tolerance band around 1/f_(M). Therefore, the switching of switch 25 is asynchronous with respect to the characteristic of the current of feed-in 21. There is no fixed phase relationship.

[0102] The switching losses of electronically designed switch 25 may be inversely proportional to switching frequency 1/T. Thus, sharply reduced switching losses result because of the large period duration T used.

[0103] The dimensioning of the link-circuit reactor is determined by the use of large period duration T, the asynchronous operation and the requirement that the link-circuit current not pulsate during operation, in order to provide a continuous power flow.

[0104] For other exemplary embodiments according to the invention, a value from a 50%-wide tolerance band around 1/f_(M) is also usable as period duration T.

[0105]FIG. 5 shows a circuit diagram of the entire overvoltage protection with generation of the driving signal as an exemplary embodiment of the present invention.

[0106] During normal operation, the overvoltage protection is not active, since the voltage at the link-circuit capacitor does not reach a critical value. If, however, in the case of an emergency, the low-voltage supply for driving electronic switch V1 fails or functions incorrectly, for example, in response to a controller defect or the like, the voltage at the link-circuit capacitor increases and may reach dangerous values. This may also happen in response to an overloading of the entire system and/or when the matching controller is under-supplied. In these cases, the overvoltage protection becomes active.

[0107] From the voltage smoothed by link-circuit capacitor C6, a voltage supply for the overvoltage-protection signal electronics, described in the following, is formed via series resistor R9 and Zener diode V8. In this context, capacitor C5 smooths the voltage applied at Zener diode V8.

[0108] The voltage divider, formed from resistors R7 and R8, generates from the link-circuit voltage a signal voltage which represents a measured value for the link-circuit voltage, evaluated by the signal electronics, and which is filtered and/or smoothed by capacitor C4.

[0109] This signal voltage is influenced, on the one hand, by the positive feedback formed from diode V7 and resistor R6, and is used on the other hand as input for shunt regulator N1.

[0110] Shunt regulator N1 essentially operates when a critical voltage value is reached. The output of shunt regulator N1 is inverted by a voltage-level converter, which is formed from transistor V6 and resistors R4 and R5, used as positive feedback (V7, R6), which increases the voltage at capacitor C4, thus at the input of shunt regulator N1, and therefore stabilizes the active state of the overvoltage protection, and is supplied to the gate of a field-effect transistor V5. This field-effect transistor V5 forms a first step for driving thyristor V4. The DC voltage and AC voltage components of the voltage at the gate of field-effect transistor V5 are brought approximatively to zero by resistor R3 and capacitor C1.

[0111] Resistor R1 stabilizes the voltage applied at the anode of thyristor V4 to the level of the smoothed voltage applied at link-circuit capacitor C6. Therefore, no unacceptably high voltage changes per time dU/dt are reached which could fire or damage thyristor V4.

[0112] Resistor R2 lowers the voltage at the gate in such a way that thyristor V4 is held in the blocked state as long as field-effect transistor V5 remains blocked. If field-effect transistor V5 becomes conductive, thyristor V4 is also fired and then shunts the link-circuit current via diode V3. Thyristor V4 only goes into the blocking state again after a drop below the holding current or disappearance of the current conducted through it.

[0113] Capacitors C2 and C3 are in turn used for interference suppression.

[0114] To summarize, the overvoltage protection thus operates in such a way that after a critical voltage at link-circuit capacitor C6 has been exceeded, thyristor V4 is fired. Only after the link-circuit voltage has dropped below the maximum allowed voltage value U_(Max) and after a drop below the holding current or disappearance of the current flowing through thyristor V4, may thyristor V4 block again.

[0115] This drop below the holding current or disappearance of the current may occur, for example, by the fact that switch V1 is switched through, or the matching controller becomes currentless.

[0116] In other exemplary embodiments of the present invention, instead of field-effect transistor V5, an IGBT, a bipolar transistor or a suitable electronic switch may be used. In addition, all parts and components may be replaced by other components which exhibit an equivalent, corresponding behavior. In particular, upon deactivation of the overvoltage protection, the forward voltage at switch V1 must be less than the sum of the forward voltages of diode V3 and of thyristor V4 upon a drop below the holding current of thyristor V4.

[0117] In further exemplary embodiments of the present invention, two or more feed-ins may also be used. In this case, the fed currents are in each instance rectified in a rectifier, smoothed in each instance by a link-circuit reactor, and brought together. Using a single switch, link-circuit current I_(Z) is either fed to the link-circuit capacitor buffering output voltage U₌ of the matching controller, or is shunted upstream of this link-circuit capacitor, depending on the power demand of the consumer connected to the matching controller.

[0118] In this way, not only two synchronously operating feed-ins, but also two asynchronously operating feed-ins are usable for supplying the matching controller.

[0119] Thus, in a first exemplary embodiment of the present invention, the transformer heads draw energy from the same line. In this case, the feed-ins operate synchronously.

[0120] In a second exemplary embodiment of the present invention, the transformer heads draw energy from two different lines. In this case, each line is supplied by one infeed controller, the frequencies of the medium-frequency current source of the respective infeed controllers having at least small deviations. The feed-ins operate asynchronously. This operation is made possible by smoothing the respective rectified current of the corresponding feed-in, using in each case a link-circuit reactor prior to bringing the currents together.

[0121] In other exemplary embodiments according to the present invention, the transformer heads draw energy from a plurality of different lines. In this case, each line is again supplied by one infeed controller, the frequencies of the medium-frequency current source of the respective infeed controllers again having small deviations. The feed-ins operate asynchronously. This operation is again made possible only by the smoothing of the respective rectified current of the corresponding feed-in, using in each case a link-circuit reactor prior to bringing the currents together.

[0122] The circuit diagrams and controls shown and described are to be understood only as schematic diagrams. The layout and alteration for practical implementation of the invention are familiar to one skilled in the art.

[0123] In other exemplary embodiments of the present invention, the medium frequency deviates from the value of 25 kHz indicated by way of example. Medium frequencies in the range of 10 kHz to 50 kHz are also technically feasible. 

What is claimed is:
 1. A method for protecting at least one consumer against overvoltages when working with a method for the non-contact transmission of electric power from one or more medium-frequency current sources, whose frequencies may have deviations around medium frequency f_(M), to the at least one moving consumer via one or more transmission lines and transformer heads, allocated to the consumers, having a downstream matching controller for adjusting the power received from the transmission line, a transmission line being supplied from a medium-frequency current source with a medium-frequency current that is constant in its effective value during the power transmission, the respective consumer being supplied with energy by at least one matching controller having at least one feed-in, one or more fed currents being rectified in each instance in a rectifier, smoothed in each instance by a link-circuit reactor, and brought together to form a link-circuit current, with the aid of a switch (S, V1), the link-circuit current, brought together in each instance, either being supplied to a link-circuit capacitor buffering output voltage U₌ of the matching controller, or being shunted upstream of the link-circuit capacitor, depending upon the power demand of the consumers, and the voltage U₌ at at least one link-circuit capacitor being compared to a fixed or predefinable value, and upon exceeding this value, an electronic power circuit-breaker (V4, Thy) being turned on for shunting the link-circuit current.
 2. The method as recited in claim 1, wherein the electronic power circuit-breaker is a thyristor which, after firing, is only blocked after there is a drop below its holding current or upon disappearance of the current shunted through it.
 3. The method as recited in at least one of the preceding claims, wherein the alternating component of the voltage applied at the thyristor does not reach any high critical values of voltage change per time dU/dt such that a firing of the thyristor is triggered because of this alternating component.
 4. The method as recited in at least one of the preceding claims, wherein the current smoothed by the link-circuit reactor does not have any high critical values of current change per time dl/dt, such that a firing of the thyristor is triggered because of this alternating component.
 5. The method as recited in at least one of the preceding claims, wherein the voltage at the switch V1 has an alternating component which is higher than the critical value of the voltage change per time dU/dt that would trigger a firing of the thyristor if this voltage were applied to the thyristor.
 6. The method as recited in at least one of the preceding claims, wherein the alternating component of the voltage applied at the switch V1 is decoupled in such a way that at the thyristor (V4, Thy), the voltage change per time dU/dt reaches no critical values such that a firing of the thyristor (V4, Thy) is triggered.
 7. The method as recited in at least one of the preceding claims, wherein the signal electronics for generating the driving signal for the electronic power circuit-breaker are supplied from the voltage at the link-circuit capacitor.
 8. The method as recited in at least one of the preceding claims, wherein the signal electronics for generating the driving signal for the electronic power circuit-breaker include a positive feedback.
 9. A device for carrying out the method as recited in at least one of the preceding claims, wherein the matching controller includes a circuit for protection against overvoltages at the link-circuit capacitor, the circuit including at least one electronic power circuit-breaker (V4, Thy), by which, in the conductive state, link-circuit current from the at least one link-circuit reactor is able to be shunted upstream of the link-circuit capacitor and/or upstream of the decoupling diode V2.
 10. The device as recited in at least one of the preceding claims, wherein the at least one link-circuit reactor is connected to the link-circuit capacitor via a diode V2.
 11. The device as recited in at least one of the preceding claims, wherein the electronic power circuit-breaker is a thyristor which, after firing, is only blocked upon disappearance of the current shunted through it.
 12. The device as recited in at least one of the preceding claims, wherein the anode voltage of the thyristor (Thy, V4) corresponds to the maximum from voltage at the link-circuit capacitor and voltage at the switch (S, V1).
 13. The device as recited in at least one of the preceding claims, wherein the anode of the thyristor is connected via a diode V3 to at least one link-circuit reactor.
 14. The device as recited in at least one of the preceding claims, wherein the anode of the thyristor is connected via a resistor R1 to the link-circuit capacitor C6. 